We ran into an issue only recently because our new building has Cisco edge switches connected to our building router via 10Gbps uplinks (each edge port is 1Gbps). Macs (10.7.x & 10.8.x) connected this way exhibit very slow (300Kbps!) SMB performance to the 7410 cluster. When connected directly to the router via 1Gig ports, or to a switch with single- or dual-connected 1Gig uplinks, performance is just fine. After some network tracing and sleuthing, we determined that it's a result of "delayed ACKs" from the Macs to the ZFSSA. By setting net.inet.tcp.delayed_ack=0 on the Macs, we get decent performance. It only happens against our ZFSSA - 10Gig connected Windows and Linux/Samba servers work just fine.
We are wondering if anyone else has experienced this, and if there was a fix on the ZFSSA that you applied to correct this. Solaris 11 appears to have a related tcp_deferred_ack_interval tuning parameter (http://docs.oracle.com/cd/E19455-01/816-0607/6m735r5ga/) that might be the right approach (but naturally the AK is "closed" so I can't test it without getting slapped!). I have a case open with Oracle, but perhaps you can help us point them in the right direction.